1. Field of the Invention
The present invention relates to an antenna and an array antenna, and more particularly, to an antenna and an array antenna capable of effectively increasing a gain of the array antenna, reducing an antenna area, and optimizing an antenna radiation pattern.
2. Description of the Prior Art
An array antenna is an antenna system composed of a plurality of identical antennas regularly arranged, and is widely used in a radar system. For space-limited applications such as automotive radar systems, designs for the array antennas are much more complicated.
In detail, an automotive radar system utilizes wireless signal transceivers disposed inside vehicle bumpers or grills to transmit or receive millimeter-wave wireless signals for ranging and information exchange applications. Since shock-absorbing Styrofoam or glass fibers are usually disposed inside the vehicle bumpers, the available space is limited. Therefore, the radar signal attenuates easily, which increases difficulty of the array antenna designs. In addition, if the automotive radar system is produced for sales of after-market, i.e. vendors for the radar systems do not participate in decision-making of materials and thickness of the bumpers, in such a condition, design requirements for the array antenna gain, the area and the radiation patterns become stricter for adapting to different cars.
In general, most automotive radar vendors utilize microstrip array antennas with coupling structures to minimize the required area. However, the operating frequency bands of the automotive radar systems are close to 24 GHz and 77 GHz. At such high frequencies, it is difficult to improve the antenna efficiency and thereby increase the antenna gain, especially with the coupling structures, since the coupling structures merely broaden the antenna bandwidth, but may affect the original beam, and cause deviation if the antenna patterns have frequency offsets. As a result, sensitivity of the transceiver in the radar system is affected, and the radar algorithm also needs to be modified in order to maintain normal radar detection.
Therefore, it is a common goal in the industry to effectively increase the array antenna gain, reduce the antenna area and optimize the antenna radiation patterns.